This section illustrates useful background information without admission of any technique described herein being representative of the state of the art.
Breath diagnostics is a fast growing trend in the medical field. Especially isotope-selective breath analysis has been applied for diagnostics and monitoring of numerous diseases and conditions, including diabetes, liver function, gastric infections and sepsis. The selectivity and sensitivity of the methods rely on precise knowledge of the isotopic composition of the exhaled gas and accordingly the determination of isotopic composition is of great interest.
Most of the currently used technologies for determining isotopic composition are based on sampling bags, wherein only a part of the breath cycle is captured, leading to decreased reliability of determination, especially as it was recently shown by the inventors that the isotopic composition changes during the exhalation cycle and, therefore, affects the determination of isotopic composition. The results on the isotope composition changing during a breath cycle have been shown in a conference paper titled “Compact, Real-Time Analyzer for C-13 and O-18 Isotope Ratios of Carbon Dioxide in Breath Air” by T. Kaariainen et. al. at the Conference on Lasers and Electro-Optics, CLEO 2016 in San Jose, Calif., United States on 5-10 Jun. 2016.
Real-time breath analysis according to the current invention, for example using an optical detector with a low volume multipass cell for example as described in an unpublished patent application of the inventors FI20155833, makes it possible to sample a correct portion of the exhaled breath and thus to tackle possible errors arising from the sampling. It is the aim of the current invention to provide a method and apparatus that mitigates for example the above problems of the state of the art and/or provides a reliable determination of composition of a gas, in particular isotopic composition of breath, or a concentration of a measured species, such as CO2, in breath.